1. Field of the Invention
The invention is concerned with the field of power semiconductor technology. It is based on a gate turn-off thyristor or GTO according to the preamble of the first claim.
2. Discussion of Background
Such a GTO essentially comprises an npnp four-layer structure and also an anode-side stop layer and is described in the published German Patent Application DE 43 13 170 A1, for example. Further GTOs with stop layer are disclosed in the U.S. Pat. No. 5,028,974 and DE 44 31 294 A1.
Gate turn-off thyristors with stop layer and homogeneous anode emitter having low efficiency, as disclosed in said DE 43 13 170 A1, for example, are usually produced with a whole-area stop layer and a whole-area anode emitter. In the blocking state, a certain reverse current then flows between anode and gate of such an element. Charge carriers are produced in the space charge zone. The resulting holes flow away through the gate terminal and the electrons through the anode. With the whole-area design of stop layer and anode emitter, the reverse-biased GTO thus constitutes an open-base transistor. The electrons flowing away through the anode lead to a voltage drop across the anode emitter. This in turn leads to injection of holes. The reverse current generated in the space charge zone is thereby additionally amplified.
The reverse current leads to heating of the GTO. However, the cooling of the silicon wafer is reduced in the edge termination region. As a result, an uncontrolled temperature rise can occur in this region. This leads to a further rise in the reverse current. The overall result of the problems described is the possibility of thermal drifting and, at the worst, destruction of the element.